Article recognition and verification

ABSTRACT

A method for checking the authenticity of a security article of the type containing magnetic particles having a magnetic saturation field H s  being greater than 100 A/m. The method includes the following steps: (a) generating an alternating field of one or more fundamental frequencies; (b) subjecting an article to be detected to the field; (c) detecting a detection signal emanating from the article to be detected; and (d) examining the detection signal for the presence of any particular higher harmonics of the fundamental frequencies or of any linear combination of the fundamental frequencies and of the harmonics, the particular harmonics or the linear combination being indicative of the presence of the magnetic particles. The method is applied at point of transaction locations, where the article to be detected is brought into close proximity with a sensor.

FIELD OF THE INVENTION

This invention concerns methods and apparatus for identifying articlesto allow verification and authentication, particularly articles formedpredominantly from non-magnetic material and incorporating magneticfibres having recognisable magnetic properties. The invention is ofparticular application in the field of high value documents such asoriginal Agreements, bank notes, value coupons, bonds, passports and thelike. However the invention is not limited to such documents and isequally applicable to the recognition and authentication of anynonmagnetic article in which identifiable magnetic particles have beenembedded.

RELATED APPLICATION

It has been proposed in EP 96203529.1 filed Dec. 12, 1996 to incorporatemagnetic particles of particular shape and magnetic properties as asecurity feature in articles which need to be recognised. Hitherto theproposal has been linked to the inhibition of photocopying of high valuedocuments such as bank notes by colour copiers and the proposal has beento incorporate a suitable sensor in a colour copier which automaticallydetects the presence of the magnetic particles or fibres in a documentplaced on the copying platen. Upon detection of such a document, thesensor is arranged to generate a signal which is utilised within thecopier to defeat the copying of the article either by inhibiting thecopying function of the machine or degrading the copy so that thearticle is not reproduced accurately by the copying process.

The detection system on the colour copiers has been achieved with amulti-sensor head mounted on a scanning carriage. The gap between thesensor and the documents is defined from a combination of the glass orplaten thickness, a tolerable gap between the scan head and the glassand the depth of focus of the optical system above the glass. This meansthat the multi-sensor has to work at a distance of a few cm. With thecombination of distance and an air core for the magnetic scanning headit was originally noted that with an acceptable coil mass, size andpower consumption this would result in a maximum magnetic field, whichwould mean that the magnetic particles would ideally need to saturatebelow 1000 A/m, i.e. have a magnetic saturation field H_(s) below 1000A/m.

The terms “magnetic saturation field H_(s)” are herein defined as theapplied magnetic field at the onset of saturation of the flux density inthe ferro-magnetic particles, above which point the variation of theflux density in the particles with the applied field becomessubstantially non-linear. In addition it was noted that saturation atthe levels of practicable fields could not be achieved unless thedemagnetisation factor N was smaller than {fraction (1/250)}, preferablysmaller than {fraction (1/1000)} in order to allow for the typicallevels of permeability which result from hard drawing materials such asPermalloy. This meant that long thin particles were needed and thatround ones would not be suitable.

The demagnetisation factor N is defined in the following well knownformula:

H _(in) =H _(app) −N×M

where M is the magnetisation of the material, H_(app) is the appliedmagnetic field, H_(in) is the magnetic field inside the material and Nis the demagnetisation factor.

Summarizing other magnetic propties, the magnetic particles had:

i) a magnetic saturation field H_(s) being greater than 100 A/m,preferably greater than 200 A/m and most preferably greater than 300A/m; this lower value is chosen not to trigger off EAS (electronicarticle surveillance) alarms

ii) a magnetic saturation flux density B_(s) being greater than 0.1Tesla;

iii) a magnetic dynamic permeability μ_(d) ranging from 10 to 10000. Theterm magnetic dynamic permeablity μ_(d) is defined here as the ratio ofthe flux density, to the magnetic field times the permeability of freespace, at the onset of saturation.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,749,946 discloses a method for checking the authenticityof a security article by detecting the magnetic resonance of anauthenticating substance at a resonance frequency.

SUMMARY OF THE INVENTION

The sensor proposed for this application is a magnetic field emittingand detection device adapted for “point of transaction” verification,e.g. where security articles are exchanged for the purpose of goods,services or money. “Point of transaction” locations may be shop tills,Banks and Building Society counters, Ticket issuing offices at railwaystations, Bureau de Change, and the like.

An object of the present invention is to provide a compact apparatuswhich includes a sensing head adapted to be brought into close proximityor actual contact with an article which is to be recognised so that anelectrical signal can be generated in response thereto forauthenticating the article which is to be presented to the sensing head.

It is also an object of the invention to provide hand held, finger, orthumb mounted devices, for use at point of transaction locationstypically in combination with a housing containing a power supply,signal processing and alarm means, for the same purpose.

It is another object of the invention to provide a method of applying asensor to articles which may or may not contain magnetic fibres orparticles to allow an electrical signal to be generated to indicatewhether or not the particles are present in the article concerned.

According to one aspect of the invention, there is provided a method forchecking the authenticity of a security article containing at least onemagnetic element such as magnetic particles having a magnetic saturationfield H_(s) being greater than 100 A/m. The method comprises thefollowing steps:

(a) generating an alternating field of one or more fundamentalfrequencies with an amplitude being greater than the saturation field ofthe magnetic element;

(b) subjecting an article to be detected to the field;

(c) detecting a detection signal emanating from the article to bedetected;

(d) examining the detection signal for the presence of any particularharmonics of the fundamental frequencies or of any linear combination ofthe fundamental frequencies and of the harmonics, the particularharmonics or the linear combination being indicative of the presence ofthe magnetic element as magnetic particles.

Or, viewed from still another angle, there is provided a method ofmaking a verifiable article which is to be detected by subjecting it toan alternating magnetic field to determine whether there is at least onespecific harmonic response generated by interaction between the articleand the field due to the non linear response of the flux density withthe applied field from particles of magnetic material associated withthe article. The method is characterised by selecting the magneticmaterial properties and the shape of the particles so that they have amagnetic saturation field greater than 100 A/m (preferably greater than300 A/m) so as to prevent triggering off electronic article surveillance(EAS) systems which also include magnetic fields, and incorporating saidparticles into the said article.

According to another aspect of the present invention, there is provideda system by which security articles can be verified, wherein authenticarticles have incorporated therein particles of a selected magneticmaterial and selected shape, the particles being saturable by analternating magnetic field thereby to generate at least one harmonic ofthe fundamental frequency of the alternating field, and wherein a sensoris provided, a first part of which generates a local alternatingmagnetic field to which articles as aforesaid are to be subjected forverification, and a second part of which generates by induction electricsignals indicative of the response of the material making up the articleto the said alternating field. Signal analysing means is provided,adapted to determine if a particular frequency, or a spectrum offrequencies, is present in the generated signals. The system ischaracterised in that the selection of the magnetic material and theselection of the shape of the particles is restricted to particles whichrequire magnetic fields in excess of 100 A/m (preferably in excess of300 A/m) before they become saturated, to prevent authentic articles asaforesaid from triggering electronic article surveillance alarms, andthe first part of the sensor generates a local field of sufficientstrength to saturate any such particles if in “close proximity” to, orin contact with, the sensor.

According to still another aspect of the invention, there is provided anapparatus for carrying out a method according to the invention or foruse in a system according to the invention.

More particularly, the invention provides a method of checking theauthenticity of an article in which a sensor is moved into “closeproximity” or contact with the article. A confirmation of authenticationsignal which may be audible or visible or vibratory or any combinationhereof is generated if magnetic particles or fibres having the requisiteproperty are detected as being present in the article.

Within the context of the present invention the terms “close proximity”mean at a distance smaller than 10.0 mm, typically smaller than 2.0 mm,e.g. at a distance smaller than 1.0 mm.

A consequence of this very small distance is that it can be possible tohave a design which could even saturate spherical particles, i.e.particles having a demagnetisation factor N smaller than ⅓, e.g. smallerthan {fraction (1/20)}.

However, a very important issue for an anti-counterfeit solution is tomake the security feature itself as difficult as possible to copy. Withthe approach proposed in EP 96203529.1, the security feature is anelongated magnetic particle such as a hard drawn metal fibre of aparticular composition and of a diameter preferably less than 30 micron.This security feature is much more difficult to imitate than sphericalmagnetic powders. Moreover, the particular characteristics of the metalfibres enable them to be virtually hidden in a substrate such as paperor plastic, not break out of the substrate with normal flexing usage andlife, and which can be made to produce a very characteristic signal. Thelatter objective is enabled by using material with a particularcoercivity, permeability and shape which provides a magnetic saturationfield substantially greater than that found in EAS gates and which issubstantially less than found with other common objects (including forexample magnetic powders.

Therefore, in a preferable embodiment of the present invention, thedemagnetisation factor N is—still—smaller than {fraction (1/250)} and ithas been found convenient to limit the magnetic saturation field toapproximately 1000 A/m to 2000 A/m at a distance of 1.0 mm above thepoles of the sensor head.

The invention also lies in a method of checking the authenticity of anarticle such as a security document in which the article is moved intoclose proximity or contact with a sensor or in which the sensor is movedinto close proximity or contact with the article.

The invention also lies in a method in which relative movement isintroduced between the article and the sensor so that if perchance aregion which is devoid of the magnetic particles or fibres is inregistry with the sensor, the movement will cause a region which doescontain the fibres or particles to be moved into proximity with thesensor either by movement of the sensor relative to the article or bythe article relative to the sensor, to allow the authentication signalto be generated.

It is of advantage if the sensor does not have to be any larger thannecessary, particularly if it is to be associated or incorporated in atill or if it is to be incorporated in a hand-held device equivalent toa pen, and since the distribution of the magnetic particles or fibresthroughout the article may not be uniform, the method involving relativemovement, between the sensor and the article overcomes the possibleproblems associated with viewing only a restricted area of the articleby a small sensor.

The method of the invention is of primary application in theauthentication of bank notes which have been printed on sheet materialcontaining the said magnetic fibres or particles. However the inventionis not limited to bank notes and the method of the invention is equallyapplicable to the authentication of any article formed from non-magneticmaterial containing the magnetic particles or fibres having the specialmagnetic properties.

In each of the methods as aforesaid, the sensor comprises a transmittingdevice which generates an alternating magnetic field of one or morefundamental frequencies and a detection system having an enhancedresponse to magnetic field variation at a frequency which is a harmonicof the fundamental frequencies or of any linear combination of thefundamental frequencies of the transmitted alternating field, and whichis a predominant component of a secondary magnetic field generated bythe magnetic particles or fibres as a result of a non-linear magneticresponse of the material forming the particles or fibres to thetransmitted alternating magnetic field.

The preferred method of the invention thus comprises the steps ofgenerating a primary alternating magnetic field at a first frequency,introducing into a region containing a concentration of magnetic flux ofthe first alternating field an article containing at least one magneticelement having a non-linear magnetisation response to magnetic fieldchanges at the frequency of the alternating field, thereby to introducea secondary field variation at at least one harmonic of the fundamentalfrequency, into the magnetic field, detecting the secondary magneticfield variation generated by the non-linear response of the magneticelement to the changes of field due to the primary alternating field,generating electrical signals at the harmonic frequency due to thesecondary magnetic field generated by the said non-linear response,selectively processing electrical signals generated by the harmonicfrequency field and characteristic of the non-linear response, asopposed to electrical signals generated by the primary alternatingmagnetic field, detecting for the presence of electrical signals at thesaid harmonic frequency and generating a signal if such signals aredetected.

An authentication signal can thus be generated if the relevant harmonicis detected in the processed signal, and the absence of any suchharmonic will result in no authentication signal being generated, whichcan be taken to indicate that there are no appropriate magnetic elements(such as fibres or particles) within the article.

According to a preferred feature of the method, inductor means isprovided proximate to an article to be detected and a generallysinusoidal electric current is caused to flow in the inductor means togenerate a primary sinusoidally varying magnetic field which links thearticle proximate thereto, input signals for the selective signalprocessing system are derived from the inductor means, and the signalprocessing system is adjusted so as not to respond to electrical signalsat the fundamental frequency of the sinusoidal alternating currentproducing the primary magnetic field, or low harmonics thereof, but tobe significantly responsive to electrical signals at frequenciesequivalent to at least one selected higher harmonic of the saidalternating current frequency. Magnetic particles or fibres situated inthe primary magnetic field are detectable if they have a non-linearmagnetic response at the fundamental frequency so as to generate asecondary varying magnetic field at the selected higher harmonic towhich the signal processing system is responsive, provided the inductormeans is also linked by magnetic flux of the secondary magnetic fieldgenerated by the non-linear response of the particles in the fibres.

In one method the inductor means comprises at least two separatewindings and the primary magnetic field producing alternating electriccurrent is supplied to one of the windings and at least one secondarywinding intimately associated with the primary winding provideselectrical signals for the signal processing system due to voltagesinduced by a linking of the secondary winding by the secondary magneticflux generated by the non-linear response particles or fibres in thearticle under test.

In a second method, a single winding may be used to which the primaryalternating current is supplied for generating the primary field andfrom which electrical signals are delivered to the processing system,which by virtue of its response, will not respond significantly toelectrical signals at frequencies close to the primary currentfrequency, but will respond to higher harmonics which will only bepresent if fibres or particles having the particular non-linearcharacteristic are linked by the alternating magnetic flux generated bythe primary currents.

The invention also lies in a sensor and an apparatus for performing theinvention as aforesaid.

In one embodiment of such an apparatus, a platform is provided on whichan article can be placed for checking, the platform incorporating atleast one sensor for generating and transmitting a primary alternatingmagnetic field towards and into the article and for responding to thesecondary alternating magnetic field returning from the article. Thealternating magnetic field returning from the article has a frequencycomponent significantly higher than the frequency of the fieldtransmitted to the article. Signal processing circuit means is providedresponsive to electrical voltages induced by the returning flux at saidhigher frequency and which is adapted to respond predominantly tosignals at that frequency to generate an authentication signal. Thiswill only occur if magnetic flux at that frequency is present in thesensor due to the returning magnetic field generated by the non linearresponse of the magnetic particles or fibres to the primary field. Theinvention could also make use of more than one of the harmonicfrequencies generated by the magnetic particles or fibres to improvesensitivity or aid in the discrimination of forgeries which try to copythe magnetic characteristics of the particle or fibres described in thisapplication.

Where the sensor is very small in cross-sectional area so that only asmall area of the article registers therewith, means may be provided formoving the sensor relative to the platform (and therefore the stationaryarticle thereon) to enable different regions of the article to bedetected by the sensor during a single test.

Alternatively the platform may be such that an article can be movedacross the surface thereof in a wiping action, such that a surface ofthe article is in close proximity with, if not in contact with thesensor located therein. In this way different regions of the articlewill be presented in succession to the sensor without the need for thesensor to be moved relative to the platform or the article thereon. Thisis of particular value where the article is a flexible sheet materialsuch as a bank note.

The platform is conveniently formed from a thin non-magnetic, e.g.plastic, sheet or membrane over the pole pieces of the sensor.Alternatively the pole pieces themselves could form the platform. In apreferred embodiment the platform is part of, or all of, the surface ofa small box which may contain the signal processing electronics and theindicator which is activated if the higher harmonic magnetic flux isdetected due to the presence of magnetic fibres or particles in thearticle under test. The indicator could be a sounder, or a lamp or both.The box could contain its own power supply or be supplied from anexternal source.

In another embodiment of the invention, a sensor may be located in theend of an elongated pen-like member which can be held between finger andthumb in the manner of a writing instrument and can be drawn across thesurface of an article to be detected as if the sensor were being used todraw a line across the said surface.

In one embodiment the invention can thus be said to provide a sensor penwhich can be picked up and used to check an article as aforesaid, andsuch a sensor pen may include a push button switch for activating thedevice so that the sensing of an article is restricted to when thebutton is depressed, for example by the user's forefinger.

The elongate pen-like device may serve to house electric circuit meansassociated with the selective signal processing or vibrator system, anda sounder, or lamp, or both, which is or are activated if the higherharmonic magnetic flux is detected due to the presence of magneticfibres or particles in the article under test. The elongate member mayalso incorporate an own supply such as a battery for powering thedevice.

Alternatively the sensor pen may be connected by a cable to a subsidiaryunit which may be a separate box containing power supply and/orelectronics and/or sounder and/or lamp, and may be a device such as acash register, or computer as used by a cashier in a bank or buildingsociety.

Alternatively the sensor may comprise a document screening device in theform of a cheque reader or the like to which a document such as apassport can be presented.

Where it is permissible to make contact with the surface of the articleand to allow light pressure to be exerted thereon, the sensor may bemounted in a separate housing which is resiliently movable relative to amain housing, and switch means is operable from an open to a closedcondition by relative movement of the sensor housing as will occur ifthe sensor housing is pressed lightly into contact with an article to bedetected or vice versa. In this way the user does not have to depress aswitch to render the device operational. The switch may comprisemechanical contacts or may be a capacitive switch which consumes littlepower. Since it is important that the switch is closed for the device tofunction correctly, the device may be adapted to produce a first tone orilluminate a first lamp when the switch is closed, and to generate asecond tone in place of the first tone (or second lamp in place of thefirst lamp) if signals at the selected higher harmonic or harmonics ofthe fundamental frequency are detected by the signal processing system.The user is thus instructed by the tone or lamps as to whether or notthe device is sensing the presence of appropriate fibres or particlesand whether or not it is necessary to shift the device over the surfaceof the article in order to try and find particles or fibres within thearticle under test.

Utilising such a sensor, the user can be instructed to listen for afirst tone and to move the sensor over the article and listen for thesecond tone. Only if the second tone is produced will the article beauthenticated by the user.

The method is relatively fail-safe since if the first tone is notproduced, the test cannot be performed in the first place, and thechange from the first tone to the second tone will only occur in thepresence of appropriate particles or fibres.

Preferably the first tone is at the first relatively low pitch and thesecond tone is at a relatively higher pitch so that it is impossible forthe user to mistakenly assume that the second tone has been produced.

According to a preferred feature of this aspect of the invention, thefirst tone is generated for a set period of time before the second tonecan be generated even if appropriate harmonic content is detected by thesignal processing system, so that the user has to listen for the firsttone, before the second tone can be generated and can be heard.

According to another feature of this aspect of the invention, the secondtone may be generated at a considerably greater power level than thefirst tone so that even in a relatively noisy environment, the secondtone will be heard.

The invention is of particular application in the field of bank notechecking and since these are regularly handled by a cashier wearing athumb or finger stall, according to another aspect of the invention, asensor as aforesaid may be incorporated in a thumb stall or finger stallwhich may also incorporate a miniature signal processing system andsignalling device, or be connected to same, as in a wrist band toindicate when magnetic particles or fibres are present in a bank notecontacted by the stall. The secondary unit housing the electronics andpower supply may include audible, visual or vibratory alarms. Theelectronics and alarms may instead or in addition be incorporated intoother equipment normally associated with the cashiers position, such asa computer or till or cash register.

Since the finger or thumb stall is of necessity brought into contactwith a note in use, pressure sensitive switch means may also beincorporated in the stall as aforesaid, and an audible tone or vibrationgenerated or a lamp illuminated in response to the detection by thesensor located in the stall of appropriate magnetic fibres or particleswithin the note in contact therewith.

In accordance with another feature of this aspect of the invention, thesignal processing system to a thumb or finger stall may alternativelygenerate an inverse of the authentication signal hitherto proposed suchthat if the stall is in contact with a note which contains appropriateparticles or fibres, no audible tone is produced by a sounder associatedtherewith (or with secondary apparatus to which it is linked), but inthe event that the stall is pressed against a note which does containsuch fibres or particles, an alarm signal is generated. In this way theoperator is not subjected to continual tones which otherwise would begenerated every time a genuine note is touched by the stall, but willonly be alerted when the stall is brought into contact with a note whichdoes not generate the appropriate response and may therefore becounterfeit note.

In accordance with a further modification of the invention, the pressuresensitive switch means associated with the sensor may be arranged toextinguish a red light and illuminate an orange light when the sensor isfirst pressed into contact with an article to be tested. The orangelight is then extinguished and a green light is produced in the eventthat appropriate particles or fibres are located as being present in thearticle, as a visual confirmation of the authenticity of the article. Analarm signal is generated in the event that with continued pressure, noparticles or fibres are sensed and the orange light is not extinguishedafter a given period of time.

According to a preferred feature of the invention, the particles are infact elongate fibres and during manufacture of the article the fibresare arranged so as to be substantially co-planar. Additionally thefibres may be orientated in a particular manner so that they are notonly all in the same plane, but all extend parallel or perpendicular toparticular directions within that plane, so that two levels ofauthentication can be provided, a first which merely detects whether ornot the fibres are present, and a second which determines theorientation of the fibres relative to the article.

Alternatively more than two levels of identification can be incorporatedwith the addition of magnetic particles or fibres having a saturationfield greater than 100 A/m but with sets of different magneticproperties e.g. saturation field strength, coercivity or dynamicpermeability.

This latter may be of advantage for authenticating specific valuedocuments such as different denomination bank notes, by arranging thatthe fibres are orientated in different directions within the sheetmaterial, from which the bank notes are produced.

Whether or not the fibres are orientated in parallel to one direction ornot, where they are substantially co-planar, albeit randomly dispersedtherein, the alternating magnetic field produced by the sensor isadvantageously arranged so that the magnetic field generated by analternating electric current is orientated substantially in the plane inwhich the magnetic fibres have their major axes, and the detector systemassociated with the sensor is arranged to pick up emissions from themagnetic fibres as they are driven through the non-linear region oftheir B-H curve by the alternating magnetic field.

Alternatives to inductive coils for detecting magnetic fields producedinclude Hall effect, magneto-resistive, magneto-inductive, flux-gate andmagneto-impedance sensors. These have an advantage over inductive coilswhere the frequencies to be detected are low, as these alternatives havea frequency response extending down to 0 Hz.

In one embodiment of sensor, an inductor is provided comprising a coilwound around the central section of a ferrite core having a so-called Esection.

In another preferable embodiment, a so-called pot core is employed, inwhich comprises a cylindrical ferrite cup incorporating a centralferrite core which has the coil wound around it. In both cases (theE-section and the pot core) where two or more windings are required,these are all located on the central section.

The advantage of the E core and pot core design is that they produce aconcentration of magnetic flux in a plane just above the exposed end ofthe central core, so that magnetic flux bridging between the centralcore and the outer ferrite section will be most concentrated in a planeparallel to the open end of the pot core. Advantageously sheet materialsuch as a bank note or other document to be detected, is located in thatplane.

The ferrite material from which the core and surrounding pot are formedis preferably selected so that it limits and preferably minimises thegeneration of harmonics of the fundamental drive field.

According to another aspect of the invention, the signal processingsystem incorporates a narrow bandpass filter restricted to one or moreof the higher harmonics of the drive magnetic field. Typically one ofthe harmonics is isolated by the use of such a narrow bandpass filter.

According to a preferred feature of the invention, a surface acousticwave filter such as is commonly used in radios may be incorporated inthe signal processing system.

The latter signal processing system advantageously may in addition to orinstead of the acoustic wave filter incorporate a phase sensitivedetector using a reference frequency locked to the primary drive fieldfrequency so ast to produce maximum rejection of unwanted frequenciesand maximum separation of desired harmonics.

Apparatus embodying the invention may be incorporated into a cashregister or till, or computer terminal as provided to a teller or clerkin a building society or bank.

The invention thus also lies in a cash register or till or computerterminal when modified to include a document reader adapted to sense thepresence within a document presented thereto of specific magnetic fibresor particles having a non-linear magnetic response to alternatingmagnetic flux at particular frequencies so as to generate in responsethereto magnetic flux at one or more harmonics of the frequency of theenergising magnetic field.

An embodiment of the invention also lies in the provision of a datalinkto a central computer by which information identifying the document suchas denomination and serial number can be stored against time and date,and till, or address, at which the forged document has been submitted,and which may also include details of the person tendering the forgednote. This information may be entered by the bank clerk or cashier, ormay be an electronic photographic representation of the person taken bya hidden camera such a miniature CCD TV camera located adjacent the tillor cash point so that an electronic image of the person tendering theforged note can be obtained and transmitted to the central computer andstored in association with the other data relating to the transaction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference tothe accompanying drawings in which:

FIG. 1 illustrates a conventional cash register;

FIG. 2 illustrates a point of sale bank note checking device linked to aconventional cash register with the sensor showing in side elevation;

FIG. 3 is a plan view of the top side of the sensor of FIG. 2;

FIG. 4 is a side elevation of an alternative bank note authenticatingdevice which may be entirely portable or used at a point of sale devicesuch as a till or cash register;

FIG. 5 is a top plan view of the device shown in FIG. 4;

FIG. 6 illustrates how a universal coupling between a probe and the mainbody of the device of FIG. 4 allows the device to be held at a moreconventional angle by the user;

FIG. 7 is a similar view to that shown in FIG. 6 with the device rotatedthrough 90° with the internal parts of the device shown as hiddendetail;

FIG. 8 illustrates another device similar to that shown in FIG. 4;

FIG. 9 is a top plan view of the device shown in FIG. 8;

FIG. 10 is similar to FIG. 7 and illustrates the internal constructionof the device shown in FIG. 8;

FIG. 11 shows how a probe can be connected to the lower end of the mainhousing of the device such as shown in FIG. 4 by means of a spring;

FIG. 12 shows the round flat underside of the probe of FIG. 11;

FIG. 13 illustrates how the spring can accommodate an acute anglebetween the axis of the probe and the axis of the main body whilstallowing the probe to remain in contact with a bank note which is beingchecked;

FIG. 14 shows the round flat underside of the probe of FIG. 13;

FIG. 15 illustrates an alternative arrangement incorporating a spring toaccommodate angular movement of the main body relative to the probe;

FIG. 16 shows the generally rectangular shape of the probe;

FIG. 17 and FIG. 18 illustrate the device shown in FIGS. 15 and 16rotated through a right angle;

FIG. 19 illustrates another embodiment of the invention in which thesensor is incorporated into a thumb stall;

FIG. 20 illustrates the magnetic flux pattern associated with an E core;

FIG. 21 shows the curve of the magnetic flux density B in a horizontaldirection 0.5 mm from the surface of an E core device

FIG. 22 is a side view of an E core device which may be used as thesensor;

FIG. 23 is a cross-section according to plane XXXI—XXXI of FIG. 24through a pot core device which has been found to be more advantageousthan an E core;

FIG. 24 is an end view of the pot core device shown in FIG. 23; and

FIG. 25 is a block schematic diagram of the electronics associated witha sensor for use as a point of transaction bank note authenticationdevice;

FIG. 26 shows an inner view of a basic apparatus for bank noteauthentication and

FIG. 27 shows an upper view of this basic apparatus.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1 cash till 110 such as used at payment locations in shops isfitted with a bank note authenticating device at 112 of the shelf 114above the till drawer 116. The authentication process involves thecashier taking each bank note in turn and pressing it on anauthenticating button of authentication device 112 and if accepted,laying or clipping the authenticating note on the shelf 114. The drawer116 opens in the normal way and change can be extracted and given to thecustomer and the authenticated notes placed in the drawer, which can beclosed ready for the next transaction.

The authenticating device is shown to an enlarged scale on FIG. 2 and itis to be understood that this could be separate from the till or asshown in FIG. 1, located at 112 on the shelf 114.

The authenticating device 112 comprises a main body 118 which may forexample house one or more batteries such as 120 and a printed circuitboard such as 122, and a lid 124 resiliently mounted on the base 118 byspring means (not shown) so as to be capable of up and down movementrelative to the base 118 as denoted by arrow 126. Within the lid 124 ismounted an electromagnetic probe 128 which generates electrical signalsfor processing by the printed circuit in the event that a bank notecontaining appropriate magnetic material is pressed against the upperpart of the lid generally designated 130.

Although not shown, a switch is provided within the two part assemblywhich is normally in the OFF mode, but when the lid 124 is pressed in adownward sense relative to the base 118, is switched into the ON-mode.

As shown in FIG. 3, light emitting diodes at 132 and 134 indicate thestatus of the sensor. Thus LED 132 is adapted to be illuminated uponpressing the lid 124 in a downward direction and LED 134 is illuminatedif the item in contact with the flat platform 130 contains appropriatemagnetic material.

A bleeper or buzzer or siren may be incorporated in the base unit 118which is adapted to sound in the event that the lid 124 has beendepressed and LED 132 has been illuminated, for more than for example 2seconds or less, and no appropriate magnetic material has been sensed.This time lag would allow the operator to slide a bank note over thesurface of the flat top 130 in case the first region registering withthe probe 128 contains insufficient magnetic material to generate theauthenticating signal.

A bank note which does not contain the appropriate magnetic materialwill not cause LED 134 to illuminate the continued pressure of the noteon the lid 124 will then result in the sounder operating therebyalerting both the cashier and the customer to the fact that the note maybe a forgery.

Although not shown, a television camera may be built into the cashregister directed towards where customers stand, and a recycling videorecorder may be connected to the video camera so that there will be avideo record of the person who has tendered a forged note, should itbecome necessary for evidence purposes.

FIGS. 4 to 18 illustrate a rather different concept. Here the sensor isin the form of an elongate pen-like device which can be held betweenthumb and fingers by the operator and various different configurationsof such device are shown.

In the arrangement shown in FIGS. 4 to 7, the pen body 136 is generallyrectangular in plan view (as shown in FIG. 5) and includes a clip 138which allows the device to be secured in a pocket or on a belt. Thehousing 136 is generally hollow and closed at its upper end by a cap 140having a power supply socket 142 and at its other end has fitted theretoa magnetic sensor 144 containing an electromagnetic probe 146 to bedescribed. The sensor housing 144 may be rigidly attached to the rest ofthe pen body 136 or more preferably attached by means of a flexiblecoupling generally designated 148.

Within the pen body 36 is located a printed circuit board 150 containingthe electronics associated with the probe 146 and one or more batteriessuch as 152 which may be rechargeable cells together with a siren orbuzzer or vibrator 154. A LED 156 is also shown in the pen body 136which indicates the status of the device.

FIG. 6 shows how the flexible coupling 148 allows the main body 136 tobe tilted relative to the sensor housing 144 whilst the latter remainsin face to face contact with a document such as a bank note 158 laidflat on a smooth support surface.

A flexible coupling allows the housing 144 to tilt relative to the penbody 136, however the latter is held, as indicated by FIG. 9, where thepen body 136 is shown with its wider width dimension co-planar with theplane in which the housing has been angled. The various items shown inFIG. 4 are identified by similar reference numerals where they appear inFIG. 7, which illustrates how a second battery 153 can be accommodatedand also illustrates a power jack 160 connected into the socket 142 forconnection via a flexible cord 162 to a separate DC source, to allow thebatteries to be charged and/or the unit to be used without a drain onthe batteries.

FIG. 7 also illustrates how an ON/OFF switch designated 164 can beincorporated in the lower region of the pen body 136 with an actuatorarm (not shown) adapted to be engaged by the probe or sensor housing 144when the pen body 136 is pressed in a generally downward sense relativeto the sensor housing 144.

Preferably the ON/OFF switch is operation into the ON mode by suchrelative movement whether the pen body 136 is angled relative to thesurface of the document 158 or not.

FIGS. 8, 9 and 10 illustrate a further arrangement in which the penhousing is generally cylindrical in cross-section as denoted byreference numeral 166 and again includes a clip 168 for securing thepen-like device in a pocket or on a belt. A status and pass or fail LEDis denoted at 170 and the electromagnetic probe 172 is mounted at thelower end of a bellows extension 174, the upper end of which is securedto the lower open end of the housing 166. The upper end of the housing166 is closed by a cap 176 which contains a power supply socket 178similar to item 142 in FIG. 4.

The bellows extension 174 is normally stretched to its maximum extent bya helical spring 180 situated within the bellows.

Contact rings 182 and 184 provide a simple arrangement for turning thedevice ON and OFF. As shown, the rings are separated and the device isOFF. By pushing the lower end of the device 186 into contact with a flatsurface such as 188 as shown in FIG. 10, and then tilting the housing166 as shown in FIG. 10, the two rings 182 and 184 come into contact andenergise the device.

The inside of the housing 166 is similar to that of FIG. 4 and samereference numerals are used to denote the similar components.

Different arrangements for a flexible coupling between a probe housing190 and a main body 192 are shown in FIGS. 11 et seq.

In FIG. 11 a helical spring 194 connects the probe or sensor housing 190to the lower end of the main housing 192 and if the latter is angled inthe plane of the paper as denoted by arrow 195, the spring 194 permitsthe two parts 190 and 192 to become angled quite significantly whilstthe underside of the probe housing 190 remains in flush contact with aflat surface such as 196.

The underside of the probe housing 190 is shown at 200 in FIG. 12.

An alternative but similar arrangement is shown in FIG. 13 in which themain housing 198 now extends in a downward sense to engage the generallypyramidal surface of the probe housing 190 and the spring 194 serves thesame purpose as in FIG. 11 but because the lower end of the housing 198is in contact with the probe housing 190, the arrangement is lesssusceptible to damage than would be the case of the arrangement shown inFIG. 11.

The underside of the probe housing 198 is shown at 200 in FIG. 14.

The arrangements shown in FIGS. 11 to 14 are of generally circularcross-section so that the angling of the main housing relative to theprobe housing can be effected in any direction.

A coiled spring flexible coupling however is not restricted to such anarrangement and a spring coupling 202 is shown in FIGS. 15 to 18 joininga generally rectangular section main housing 204 to a similar generallyrectangular probe housing 206 the cross-section of which is best seen inFIG. 18. The arrangement is such that the main housing 204 can be angledso as to adopt the position shown at 208 in FIG. 15, and 210 in FIG. 17whether it is being angled with its major dimension parallel to the axisof pivoting or perpendicular thereto as in FIG. 17.

FIG. 19 illustrates a further development of the invention in which anelectromagnetic probe shown in dotted outline at 212 is incorporatedinto a thumb stall 214 adapted to be worn by a cashier. The stallincludes a flexible link 215 connecting it to a wrist band 216 similarto a wrist watch and in place of the watch a housing is carried by thewrist band at 218 within which is located the electronics, a battery anda vibratory device.

The latter may produce a sound or may simply be arranged to vibrateagainst the wrist of the user.

In a first mode the electronic circuit may be adapted to cause thevibration if a note in contact with the thumb stall is genuine (i.e.contains appropriate magnetic material). In a second alternative mode itonly vibrates if the note is a counterfeit.

In either event, if only to conserve power, an ON/OFF membrane switch220 is incorporated into the thumb stall so that the probe 212 is onlyrendered sensitive when the finger stall is pressed against a bank noteor other device to be authenticated.

The wrist section preferably includes a membrane switch to allow theuser to turn off the vibration once this has occurred, where the deviceis operating in the second mode, i.e. where the thumb stall membraneswitch has been closed by pressure against a surface but no magneticmaterial has been sensed by the probe 212.

By arranging that the device merely vibrates but makes no sound, thecashier is alerted to the fact that the note may be a forgery withoutnecessarily alerting the customer to the fact that this has been notedby the cashier.

The device may be used by an operator at a point of sale for checkingmoney, for document handling as in the case of passports and the like,for packaging inspection where particular security packaging material isto used to validate packages, or in the case of ticket inspection, whereappropriate magnetic materials has been incorporated into the tickets,and allows an inspector to verify that document is genuine in a covertmanner.

Although shown as thumb stall, the device shown in FIG. 19 may bereadily adapted alternatively as a finger stall to facilitate a bankclerk or teller who is counting and checking bundles of notes. In thisevent the response time of a vibrator on the wrist may not beappropriate and an alternative short response time alerting system wouldbe required based on the operation of the ON/OFF membrane in the thumbor finger stall and the absence of a confirmatory signal from the probe,which will only exist if the material in contact with the thumb stall orfinger stall contains the appropriate magnetic material. In this eventan alarm can be sounded almost instantaneously so that a teller who israpidly counting or checking a bundle of notes will be alertedinstantaneously if one of the notes which is being fingered fails toproduce the appropriate magnetic and electrical response.

The probe 212 needs to be connected to the wrist band and to this end acable 222 is shown in dotted outline. By providing this on the inside ofthe hand, so it will be less evident that the thumb or finger stall isanything other than a conventional one.

The invention relies on a very sensitive electro-magnetic probe for itssuccess. A large air-cored coil is not preferred and it has been foundmost appropriate to use a ferrite-cored coil. One type of former forsuch coil is an E core, that is a ferrite core in the configuration of acapital E with windings around the central stem of the E. The fluxpattern associated with such a core is illustrated in FIG. 20 asreference number 224 and a security document to be detected is referredto as 226. The magnetic flux density B in function of position x for anE core device 0.5 mm from the end of the core is shown in FIG. 21.

An E core is shown at 228 in FIG. 22 and the drive coil is shown at 230and the sensing or detection coil is shown at 232. Two such coils areused where it is desired to cancel out the main fundamental component ofthe magnetic field originating from the drive coil. Where the subsequentelectrical signal processing has a sufficiently narrow bandwidth, andlow frequency rejection, this may not be necessary and it is also deemedpossible that a single coil may be used in practice instead of twocoils.

A pot core device which distributes the field in an annular ring int hesensing plane is shown in FIGS. 23 and 24. A pot core is formedeffectively by rotating an E core about its central axis of symmetry.The resulting configuration comprises a central cylindrical stem 234surrounded by a cylindrical sleeve 236 joined at the base by acylindrical plate 238. In practice, the arrangement may be formedintegrally, or from separate components as desired.

A cross-section through the pot core of FIG. 24 is shown in FIG. 23 andtwo separate windings of the drive coil 240 and detection 242 are shown.

FIG. 25 is block schematic diagram of the electronic circuitryassociated with two coils such as 240 and 242.

The drive current for coil 240 is derived from a sinusoidal oscillator244 which may include a power output stage, and the detection coilsignals are supplied via buffer amplifier and high pass filter 246 to anarrow bandpass filter 248. The latter may be a SAW filter. The filteredoutput from 248 is amplified by a high gain amplifier 250 and, as theelectrical coupling between the previous stages of the electronics ispreferably AC coupled, the output is rectified and low pass filtered orintegrated by means of 252 and 254 to provide an average DC signal whichis compared with a DC threshold in detector 256 to determine over aperiod of time equal to a few cycles of the harmonic whether or notappropriate signals have been passed by the bandpass filter 248 toindicate that the detection coil 242 is responding to a magnetic fieldoscillating at the appropriate harmonic of the sinusoidal oscillator244. If so, the threshold detector 256 cause a bleeper or signal lamp258 to operate to indicate that the item is in contact with thedetection coil contains appropriate magnetic material.

In an alternative version of the circuit the rectifier 252 is replacedby a phase sensitive detector which is phase locked to the oscillator244.

FIG. 26 and FIG. 27 show a very compact and simple version of anapparatus for use in the invention. The apparatus is suitable for usefor bank note authentication. The apparatus may be used as a stand aloneunit at any location or it could conveniently be located adjacent to atill in a shop or adjacent to a computer terminal in a bank or buildingsociety. The unit comprises a box 260 with a thin walled plastic portionat 262 (not shown as thin on the diagram) over a sensor 264 withmagnetic poles at 265 behind a locating spot 266, which could be printedon the surface of the box 260. The box 260 contains a printed circuitboard 268 with signal processing electronics 270, a visible lightindicator 272, and an audible bleeper 274. The unit may be selfcontained for its power supply via a power cord 276. The authenticationprocess involves the user placing a note on, or wiping a note across thelocating spot 266. A genuine note containing the special magneticparticles will give a signal which causes the bleeper to sound and thelight indicator to illuminate.

The magnetic material and incorporation of such material in sheetmaterial such as security document paper is preferably as described inEuropean Patent Application No. 96203529.1 filed on Dec. 12, 1996.

What is claimed is:
 1. A method for checking the authenticity of asecurity article, said security article containing a plurality ofrandomly dispersed magnetic metal fibers, said method comprising thefollowing steps: (a) generating an alternating field of one or morefundamental frequencies with an amplitude being greater than thesaturation field of the magnetic metal fibers of the security article;(b) subjecting the security article to be detected to said field; (c)detecting a detection signal emanating from said security article to bedetected; and (d) examining the detection signal for the presence of anyparticular harmonics of said fundamental frequency or said fundamentalfrequencies or of any linear combination of said fundamental frequenciesand of said harmonics, said particular harmonics or said linearcombination being indicative of the presence of the plurality ofrandomly dispersed magnetic metal fibers.
 2. A method according to claim1 wherein said magnetic metal fibers have a saturation field H_(s) of atleast 100 A/m.
 3. A method according to claim 2, wherein said magneticsaturation field is greater than 200 A/m.
 4. A method according to claim3, wherein said magnetic saturation field is greater than 300 A/m.
 5. Amethod according to claim 1, wherein said alternating field is ofsufficient strength to cause a substantial nonlinear response in fluxdensity in the magnetic element or magnetic metal fibers to generatesaid harmonics.
 6. A method according to claim 1, wherein the detectionsignal is constituted by electrical signals, said method furthercomprising the step of selectively processing said electrical signals atsaid particular harmonic frequencies in preference to signals at otherfrequencies, detecting for the presence of signals in the output of thesaid selective processing and generating an authentication signal inresponse to the said detection.
 7. A method according to claim 1,wherein said generated alternating field has only one fundamentalfrequency.
 8. A method according to claim 1, wherein said magnetic metalfibers have a demagnetisation factor smaller than {fraction (1/20)}. 9.A method according to claim 8, wherein said magnetic metal fibers have ademagnetisation factor N smaller than {fraction (1/250)}.
 10. A methodaccording to claim 1, wherein said alternating field is a local fieldoperating in close proximity to the article to be detected.
 11. A methodaccording to claim 10, wherein said local field is generated by means ofa sensor and wherein said sensor is brought into contact with saidarticle to be detected or wherein said article to be detected is broughtinto contact with said sensor.
 12. A method according to claim 11,wherein a relative movement is introduced between said sensor and saidarticle to be detected, so that if perchance a region which is devoid ofsaid magnetic metal fibers is in registry with the sensor, the movementwill cause a region which does contain said magnetic metal fibers to bemoved in registry with the sensor.
 13. A method according to claim 12,wherein said movement involves a wiping action of said sensor withrespect to said article to be detected or vice versa to enable differentregions of the article to be detected by the sensor.
 14. A methodaccording to claim 11, wherein said method further comprises an initialstep of activating said sensor so that checking of an article isrestricted to when said sensor is activated.
 15. A method according toclaim 1, wherein said method comprises a step of producing anauthentication signal in case magnetic metal fibers are detected in atleast one region of said article to be detected.
 16. A method accordingto claim 15, wherein a visual authentication signal is produced.
 17. Amethod according to claim 16, wherein said method comprises the stepsof: a) causing a first lamp to operate when said sensor is activated andwhen no magnetic metal fibers are detected; and b) causing a second lampto operate when magnetic metal fibers are detected.
 18. A methodaccording to claim 15, wherein an audible authentication signal isproduced.
 19. A method according to claim 18, wherein said methodcomprises the steps of: a) producing a first tone when said sensor isactivated; and b) producing a second tone in place of the first tonewhen magnetic metal fibers are detected.
 20. A method according to claim19, wherein said first tone and said second tone are at substantiallydifferent pitches.
 21. A method according to claim 19, wherein saidfirst tone and said second tone are at substantially different powerlevels.
 22. A method according to any one of claim 19, wherein the firsttone is produced for a set period of time before the second tone can begenerated so that any user has to listen initially to the first tone.23. A method according to any one of claim 15, wherein a vibratoryauthentication signal is produced.
 24. A method according to claim 1,wherein said method comprises a step of producing an alarm signal incase no magnetic metal fibers are detected in said article to bedetected.
 25. A method according to claim 1, wherein said one or eachsaid fundamental frequency lies above 1 kHz.
 26. An apparatus adaptedfor carrying out a method for checking the authenticity of a securityarticle according to claim 1, said security article containing at leastone magnetic element, said apparatus comprising: a) means for generatingan alternating field of one or more fundamental frequencies with anamplitude being greater than the saturation field of the magneticelement; b) means for detecting a detection signal emanating from saidarticle to be detected; and c) means for examining the detection signalfor the presence of any particular harmonics of said fundamentalfrequency or said fundamental frequencies or any linear combination ofsaid fundamental frequencies and of said harmonics, said particularharmonics or said linear combination being indicative of the presence ofsaid magnetic element.
 27. An apparatus according to claim 26, saidapparatus comprising an inductor for generating said alternating fieldand for detecting said detection signal.
 28. An apparatus according toclaim 27, wherein said inductor comprises at least two separatewindings, a first winding being associated with said alternating fieldand a second winding being associated with a field emanating from saidarticle to be detected.
 29. An apparatus according to claim 28, whereinsaid winding or windings are wound around a ferrite core.
 30. Anapparatus according to claim 29, wherein said ferrite core has anE-section.
 31. An apparatus according to claim 29, wherein said ferritecore is a pot core.
 32. An apparatus according to claim 27, wherein saidinductor comprise a single winding being associated with both saidalternating field and a field emanating from said article to bedetected.
 33. An apparatus according to claim 26, wherein said apparatuscomprises a Hall effect device.
 34. An apparatus according to claims 26,wherein said apparatus comprises a magneto-resistive device.
 35. Anapparatus according to claim 26, said apparatus comprising means forexamining the detection signal, wherein said means comprises a narrowbandpass filter restricted to one, or to a group, of the harmonics ofthe source signal.
 36. An apparatus according to claim 35, wherein saidmeans for examining the detection signal comprises a surface acousticwave filter.
 37. An apparatus according to claim 26, wherein said meansfor examining the detection signal comprises a phase sensitive detectorso as to produce maximum rejection of unwanted frequencies and maximumseparation of desired harmonics.
 38. An apparatus according to claim 26,wherein said apparatus further comprises means for producing anauthentication signal.
 39. An apparatus according to claim 26, whereinsaid apparatus further comprises a document screening device to which adocument to be detected can be presented.
 40. An apparatus according toclaim 26, wherein a sensor comprises means for activating the apparatusso that the checking of an article is restricted to when the apparatusis activated.
 41. An apparatus according to claim 40, wherein said meansfor activating the apparatus comprise a switch operable from open toclosed condition if the apparatus is pressed into contact with thearticle to be detected or vice versa.
 42. An apparatus according toclaim 26, wherein the apparatus is part of a portable device suitablefor being held in a hand.
 43. A portable device according to claim 42,wherein said device is in the form of an elongate pen-like member.
 44. Ahand-held device according to claim 42, wherein said device is in theform of a thumb stall or finger stall.
 45. An apparatus according toclaim 26, said apparatus further comprising a platform on which thearticle to be detected can be placed.
 46. An apparatus according toclaim 45, further comprising means for moving said sensor relative tothe platform to enable different regions of the article to be detected.47. An apparatus according to claim 26, wherein the apparatus is a partof a cash register.
 48. An apparatus according to claim 26, wherein theapparatus is a part of a computer terminal.
 49. An apparatus accordingto claim 26, wherein the apparatus is a part of an automatic vendingmachine.
 50. An apparatus according to claim 26, wherein the apparatusis a part of an automatic bank note counting machine.
 51. An apparatusaccording to claim 26, wherein the apparatus is a part of a bank notechecking machine.
 52. A method of making a verifiable article which isto be detected by subjecting it to an alternating magnetic field todetermine whether there is at least one specific harmonic responsegenerated by interaction between the article and the field due to thenon-linear response of the flux density with the applied field fromrandomly dispersed metal fibers of magnetic material associated with thearticle, said method comprising the step of selecting the magneticmaterial properties and the shape of the metal fibers so that they havea magnetic saturation field greater than 100 A/m so as to preventtriggering off electronic article surveillance (EAS) systems which alsoinclude magnetic fields, and incorporating said randomly dispersed metalfibers of magnetic material into the said article.
 53. A method as inclaim 52, wherein: a) the step of selecting includes the selection ofthe said magnetic material and the selection of the said shape beingrestricted to metal fibers which require magnetic fields in excess of300 A/m before they become saturated.
 54. A system by which securityarticles can be verified, wherein authentic articles have incorporatedtherein randomly dispersed metal fibers of a selected magnetic materialand of a selected shape, said randomly dispersed metal fibers beingsaturable by an alternating magnetic field thereby to generate at leastone harmonic of a fundamental frequency of the alternating field; andwherein a sensor is provided, a first part of which generates a localalternating magnetic field to which articles as aforesaid are to besubjected for verification, and a second part of which generates byinduction electric signals indicative of the response of the materialmaking up the article to the said alternating field; a signal analysingdevice is provided, configured to determine if a particular harmonic ora spectrum of harmonics, is present in the generated signals; theselection of the said magnetic material and the selection of the saidshape is restricted to metal fibers which require magnetic fields inexcess of 100 A/m before they become saturated, to prevent authenticarticles as aforesaid from triggering electronic articles surveillancealarms, and the first part of the sensor generates a local field ofsufficient strength to saturate any such metal fibers if in closeproximity to, or in contact with, the sensor.
 55. A system as in claim54, wherein: a) the selection of the said magnetic material and theselection of the said shape is restricted to metal fibers which requiremagnetic fields in excess of 300 A/m before they become saturated.